1 On our planet Earth, life comes in a variety of forms. We have about 2 million species of animals (such as elephants). We have about 270,000 types of plants (such as sunflowers). We have about 4,000 kinds of bacteria (such as E. coli). We have about 80,000 different protists (such as algae). And we have about 72,000 assorted fungi (such as mushrooms). What do all these organisms or living things have in common? As hard to believe as it is, they are made of the same thing - the cell. Some like animals and plants consist of many or even trillions of cells, while others like protists and bacteria are a single cell.2 Robert Hooke was the first scientist to solve this great mystery of life. When he observed a thin slice of cork under a microscope in 1663, he noted that the cork looked like hundreds of tiny boxes or a honeycomb. Hooke called these tiny boxes "cells", which means "little rooms" in Latin. What Hooke did not realize at the time is that he was actually looking at the walls or outer layers of cells, not inside cells themselves. Nearly two hundred years had elapsed before any scientist made any new, significant breakthrough. The hard work put in by scientists of the 19th century derived the so-called Cell Theory: